The present invention relates to the field of housings used in rolling bearings for maintaining a uniform circumferential spacing between their rolling elements.
Housings have been used for many years which are made of synthetic material such as 6,6-polyamides, if appropriate reinforced with glass fibres in order to increase their. mechanical characteristics, and which have many advantages including the ease with which they can be produced by injection moulding, the ease with which they can be installed by latching, their low level of operating noise and their lightness.
Such housings made of synthetic material are, of course, intended for uses where the rolling bearings can be induced to rotate at extremely high speeds. For example, for rolling bearings having small dimensions, with an outside diameter in the region of ten millimeters, these speeds may be of the order of one hundred thousand revolutions per minute.
The development of current techniques is tending to increase even further the rotational speeds to which the rolling bearings are subjected in continuous operation, so that problems arise which the housings known at the present time do not make it possible to solve.
More particularly, the housings used at the present time are generally in the form of a ring delimited radially by two substantially cylindrical surfaces concentric to their axis of rotation and axially by a front surface and a rear surface which are perpendicular to the axis of rotation of the housing.
This ring has spherical cells issuing radially on the outside and on the inside and axially in a direction through the said front surface. Each cell is prolonged by a pair of tabs arranged face to face and between them defining an orifice, through which a ball can be introduced axially into the cell by latching. The inner surfaces of the tabs of the cells encase the balls axially and radially in both directions, in order at the same time to ensure the retention of the housing on the row of balls and the spacing between the balls.
It was found that, at high rotational speeds, a conventional polyamide housing is subjected to pronounced deformation due to the centrifugal force, thus giving rise, in particular, to the following problems.
The cells undergo considerable deformations, thus bringing about an increase in the plays between the balls and the cells in the outer part of the latter and, on the contrary, a tendency for the cells to constrict on the inner parts of the balls.
The balls come in contact with the tabs mainly in their zones located towards the bore of the housing, thus giving rise to high friction and contact pressures between the housing and the balls.
This high friction and these high contact pressures increase the dissipation of energy, raise the temperature, destroy the lubricant film, increase wear and promote the detachment of microparticles from the. housing.
The situation may arise, furthermore, where the radial deformation of the housing causes contacts between this housing and the outer raceway of the rolling bearing.
It was also possible to note that, at high operating speeds, instability phenomena occur in the behaviour of the housing, along with in particular the appearance of vibratory phenomena, which are attributable to the fact that the centre of gravity of the housing is generally offset axially relative to the radial plane defined by the centres of the balls.
The phenomena which have just been mentioned lead, at very high speeds, to the rapid destruction of conventional cages and consequently of the rolling bearings.
The object of the present invention is to provide a housing device making it possible at least partially to overcome the disadvantages of conventional housings, in order to ensure improved operation of, in particular, ball-type rolling bearings equipped with such housings, and to increase their service life, especially when these rolling bearings are expected to operate at very high rotational speed.
The annular housing device according to the invention, intended for maintaining the circumferential spacing of the rolling elements, in particular balls, in a rolling bearing, comprises at least one row of balls arranged between two rolling tracks, the said housing having a rear face and a front face which are axially offset and having a multiplicity of substantially spherical cells, in each of which a ball is arranged, the said cells issuing axially on the said front face and radially on the two sides, the said front face having a multiplicity of pairs of opposite tabs for maintaining the said balls in the said cells.
According to the invention, the said front face comprises two surfaces axially offset relative to one another, of which a first surface has the said tabs projecting axially from it and is located in a plane in front of the radial plane passing through the centres of the said cells, and of which a second surface is located in a plane passing substantially through the centres of the said cells.
According to the invention, the said first surface is located radially outside the said second surface.
According to the invention, the said tabs are preferably arranged in such a way that contact between them and the balls is made in a zone located outside a virtual cylindrical surface of the same axis as the said housing and passing through the centres of the said cells.
According to the invention, the said tabs are preferably arranged in such a way that their free ends are located outside a virtual cylindrical surface of the same axis as the said housing and passing through the centres of the said cells.
According to the invention, the ratio between the radial thickness of the said tabs and the total radial thickness of the said housing is preferably between 0.45 and 0.6.
According to the invention, the ratio between the axial length of the said tabs and the thickness of the said housing from its rear face to the end of the said tabs is preferably between 0.07 and 0.33.
According to the invention, the original diameter passing through the centres of the said cells is preferably smaller than or equal to the original diameter of the rolling bearing passing through the centres of the balls.
According to the invention, the radial offset between the original diameter passing through the centres of the said cells and the original diameter of the rolling bearing passing through the centres of the balls is preferably between zero and one quarter of the diameter of the balls.
According to the invention, the said rear face of the housing preferably comprises at least one annular recess.
According to the invention, the bottoms of the cells are preferably provided with through-passages.
According to the invention, the said rear face of the housing preferably comprises an outer annular rib and an inner annular rib which are separated by an annular recess.
According to the invention, the bottom of the said recess preferably comprises convex parts in the zones of the cells and flat parts between these convex parts.
According to the invention, the said outer radial surface and the said inner radial surface meet preferably in a concave rounding.
According to the invention, the axial thickness of the said ribs is preferably reduced in the zone located between and at a distance from the said cells.
According to the invention, the ratio between the axial offset between the said outer and inner axial surfaces and the diameter of the balls is preferably between 0.05 and 0.33.
Another subject of the present invention is a ball-type rolling bearing comprising a housing device, such as has just been presented.